This invention relates to a method of managing data stored in a storage system, and more particularly, to a data management method using a differential snapshot technique.
In a computer system, data stored in a storage system may be duplicated for backup or checking of the data. Examples of a method of duplicating data include a method of copying all data to another data area. However, the copy method requires data storage area having a large size in order to store both source data and destination data. Therefore, a so-called differential snapshot technique is used to duplicate data virtually by managing only data update differentials.
When using the differential snapshot technique, two data storage areas are set in the storage system. One data storage area is called a primary volume, and the other data storage area is called a differential volume. The primary volume stores the source data. In a case of updating data stored in the primary volume, data that has not been updated is evacuated to the differential volume. To refer to the destination data, it is first checked whether or not the data is evacuated to the differential volume. When it is determined that the data has been evacuated, the data stored in the differential volume is referred to. When it is determined that the data has not been evacuated, the data stored in the primary volume is referred to. Further, when updating the data stored in the differential volume, an updated piece of the data is stored in the differential volume.
The differential volume stores only the updated piece of data, thereby having a small size. Accordingly, by using the differential snapshot technique, data can be duplicated virtually without using a large-size data storage area.
An example of such the differential snapshot technique is disclosed in JP 2004-272854 A. A known technique related to a data evacuation is found in an article written by Kazuo Goda, Takayuki Tamura, Masato Oguchi, and Masaru Kitsuregawa, and titled “Run-time Load Balancing System on SAN-connected PC Cluster for Dynamic Injection of CPU and Disk Resource. . . . A Case Study of Data Mining Application . . .” on pages 182-192 of Proceedings of 13th International Conference on Database and Expert Systems Applications (DEXA 2002), which was issued in September 2002.